Children’s white blood cell counts in relation to developmental exposures to methylmercury and persistent organic pollutants

•White blood cell counts may be affected by developmental exposure to immunotoxicants,.•We assessed associations of latent pollutant exposures with cell counts at age 5 years,.•Prenatal methylmercury exposure was associated with depleted white cells, especially lymphocytes,.•Perfluorinated compound exposures at age 5 were associated with higher basophil counts,.•White cell counts appear to be affected in different ways by immunotoxicant exposures. To explore possible markers of developmental immunotoxicity, we prospectively examined 56 children to determine associations between exposures to methylmercury and persistent organic pollutants since birth and the comprehensive differential counts of white blood cells (WBC) at age 5 years. Extended differential count included: neutrophils, eosinophils, basophils, lymphocytes (includingT cells, NK cells, and B cells), and monocytes. Organochlorine compounds (OCs) including polychlorinated biphenyls (PCBs) and pesticides, five perfluoroalkyl substances (PFASs), and total mercury (Hg) were measured in maternal (n=56) and children’s blood at 18 months (n=42) and 5 years (n=54). We constructed latent functions for exposures at three different ages using factor analyses and applied structural equation models adjusted for covariates. Prenatal mercury exposure was associated with depleted total WBC, especially for lymphocytes, where a one standard deviation (SD) increase in the exposure was associated with a decrease by 23% SD (95% CI: −43, −4) in the cell count. Prenatal exposure to OCs was marginally associated with decreases in neutrophil counts. In contrast, the 5-year PFASs concentrations were associated with higher basophil counts (B=46% SD, 95% CI: 13, 79). Significantly reduced subpopulations of lymphocytes such as B cells, CD4-positive T helper cells and CD4 positive recent thymic emigrants may suggest cellular immunity effects and dysregulation of T-cell mediated immunity. Developmental exposure to environmental immunotoxicants appears to have different impacts on WBC counts in childhood.